Retaining arrangement for a bearing, in particular for a high pressure compressor shaft

ABSTRACT

A retaining arrangement is provided for retaining a bearing around a stub shaft having a machined cavity and which includes a ring forming a stop for the bearing nut and a locking piece.

TECHNICAL FIELD

Described is an arrangement for retaining a bearing, designed inparticular to support a high-pressure compressor shaft, without thisapplication be restrictive.

BACKGROUND ART

The construction of turbomachines demands complicated layouts because ofthe nesting of the high-pressure compressor and turbine stage inside thelow-pressure turbine and compressor stage and because of the presence oftwo concentric runs of shafts each of which connects the compressor ofone stage to the corresponding turbine. This complication is encounteredabove all during machine maintenance, when the machine has to bedisassembled then reassembled.

A particular problem arises in the case of the high-pressure compressor.If we examine FIG. 1, which depicts an aircraft engine in longitudinalsection, a rotor 1 is engaged in the center of a stator 2 andconventionally comprises a fan 3, a low-pressure compressor 4, ahigh-pressure compressor 5, a high-pressure turbine 6 and a low-pressureturbine 7 which are aligned from front to rear. All of these elementscarry blades which alternate with stationary vanes of the stator 2 and,like those, are located in an annular stream 8 through which the gasesflow; a combustion chamber 9 is arranged in the annular stream 8 betweenthe high-pressure turbine 6 and compressor 5, and allows the fuelinjected further upstream in the stream 8 to be burnt and thus producecombustion gases which drive the turbines 6 and 7. There is also a runof high-pressure shafts 10 connecting the high-pressure compressor 5 tothe high-pressure turbine 6 and a run of low-pressure shafts 11extending into a cavity 12 of the previous run of shafts 10 and whichconnects the low-pressure compressor 4 to the low-pressure turbine 7.

The high-pressure run of shafts 10 comprises, in particular, ahigh-pressure compressor stub shaft 13 around which is engaged a bearing14 which supports it via a rib 15 belonging to the stator 2. Referringto FIG. 2 now for a more detailed examination, it can be seen that thebearing 14 is a rolling bearing, the inner ring 16 of which is slippedaround the stub shaft 13 and held in place by a stop ring 17, it toobeing slipped around the stub shaft 13 from its end face 18 and whichpresses the inner ring 16 backwards, against an opposed stop ring 19which touches a step 20 of the stub shaft 13. The inner ring 16 is keptclamped between the stop rings 17 and 19 by a nut 21 which, on itsinterior face, has a screw thread 22 engaged in a screw thread 23 madeon the stub shaft 13 near the end face 18: by tightening the nut 21, thestop ring 17, the inner ring 16 and the opposite stop ring 19 are pushedback in turn before this stack of components is compressed against thestep 20. The arrangement is supplemented by a locking piece 24, thepurpose of which is to prevent the nut 21 from working loose as a resultof vibration; this locking piece 24 is engaged in the cavity 12 and heldin place in the stub shaft 13 by a circle of splines 25 engaged incorresponding splines belonging to the stub shaft 13 and by curved-overends 26 of flexible tabs 27 engaged in a groove 28 in the stub shaft 13.The first of these connecting means prevents the locking piece 24 fromrotating and the second prevents its translational movement, withrespect to the stub shaft 13. The flexible tabs 27 are furthersupplemented by engagement tongues 29, adjacent to the curved-over ends26. However, the locking piece 24 also comprises a circle of teeth 30,protruding from the cavity 12 and which engage between complementaryteeth 31, also arranged in a circle and produced on a portion 32 of thenut 21 which extends inwards, in front of the end face 18 of the stubshaft 13, which it covers. For the sake of preciseness, it is added thatthe teeth 30 are at the front of the locking piece 24, the flexible tabs27 at the rear, and the curved-over ends 26 and the engagement tongues29 at the rear of the tabs 27.

To remove the high-pressure compressor 5 to which the stub shaft 13belongs, this shaft needs to be disengaged from the bearing 14. Apreliminary step consists of removing the low-pressure turbine 7 so thata high-pressure turbine shaft 33 which belongs to the line oflow-pressure shafts 11 and occupies most of the cavity 12 can beextracted, by pulling it backwards. An appropriate tool with claws isthen inserted around the engagement tongues 29 to press against them andpush them all towards the axis of the machine by curving the flexibletabs 27, whereby the curved-over ends 26 come out of the groove 28 andthe locking piece 24 can then be pulled backwards to extract its splines25 from the splines of the stub shaft 13 and to disengage its teeth 30from the teeth 31.

It would then seem possible to unscrew the nut 21 using a tool engagedbetween the teeth 31, but such an operation is actually prematurebecause a low-pressure compressor shaft 34, also belonging to the run oflow-pressure shafts 11, has remained in place and extends just in frontof the nut 21: the axial space denoted I which separates them is smallerthan the length, denoted J, by which the nut 21 is engaged on the stubshaft 13. It is therefore necessary also to remove the low-pressurecompressor 4 and its shaft 34 before the high-pressure compressor 5 canbe removed, this being an operation which is not necessarily useful.What is more, removing the low-pressure compressor 4 itself may becomplicated and need to be preceded by the removal of other parts of themachine, for example a gearbox which has not been depicted in thefigures. All of this means that removing the high-pressure compressor 5is a lengthy and tiresome operation that cannot be made any easier byenlarging the space I, as this would entail reviewing the entire designof the machine and would increase its size.

DISCLOSURE OF THE INVENTION

The object of the invention therefore consists in facilitating theremoval of such an arrangement for retaining a bearing comprising astop, a clamping nut and a locking piece by reducing the preliminarymanual interventions intended to free these parts, so that the bearingcan be separated from the stub shaft it supports. The advantages of theinvention are obvious with an arrangement of runs of shafts such as theone just described because there is no longer the need to remove partsin front of the front end of the stub shaft, and access to just one sideof the retaining arrangement, from which the stub shaft will be removed,will suffice. To do this, a novel type of retaining arrangement isproposed. In its most general design, the arrangement, arranged around astub shaft in which is machined a cavity and which is bounded by an endface, comprises a ring forming a stop for the bearing, a nut forclamping the ring and a piece for locking the nut, the locking piecebeing held in the cavity of the stub shaft by removable means ofattachment and connected to the nut by imbricated teeth arranged in acircle on the nut and on the locking piece, and it is characterized inthat the ring comprises an interior portion covering the end face of thestub shaft as far as the cavity and equipped with a screw thread forscrewing onto a thread of the nut, and the nut is placed in the cavityand comprises a stop face directed towards the end face and engagedagainst a stop face standing up from the stub shaft in the cavity.

Further light will be shed on the nature of this new arrangement and onits advantages using the following figures, in addition to FIGS. 1 and 2already described and which depict a turbomachine and that portionthereof which bears a conventional retaining arrangement.

BRIEF DESCRIPTION OF THE DRAWINGS

Various other objects, features and attendant advantages of the presentinvention will be more fully appreciated as the same becomes betterunderstood from the following detailed description when considered inconnection with the accompanying drawings in which like referencecharacters designate like or corresponding parts throughout the severalviews and wherein:

FIG. 1 shows a conventional aircraft engine;

FIG. 2 shows additional details of the engine shown in FIG. 1;

FIG. 3 is similar to FIG. 2 but illustrates the inventive arrangement ofthe present invention,

FIG. 4 is a perspective view of the novel nut and of its locking piece,and

FIG. 5 illustrates a new locking piece which can be used in place of theprevious ones.

BEST MODES FOR CARRYING OUT THE INVENTION

Several of the elements of FIG. 2 are found again in FIG. 3,particularly those bearing the numbers 11, 12, 14, 15, 16, 18, 19, 20,33 and 34, such that a repeat description thereof will not be given.There is also a high-pressure compressor stub shaft and a locking piece,but these pieces here are referenced as 113 and 124 because they differin a number of ways with respect to appearance and proportions bycomparison with the corresponding parts 13 and 14 of the known design;further, the retaining arrangement also comprises a stop ring 117 and anut 121, but which are fairly different from the corresponding parts 17and 21 already described. Specifically, the stop ring 117 extends beyondthe stub shaft 113 and has a portion 40 covering the end face 18 of thestub shaft 113 and extending as far as in front of the cavity 12, likethe portion 32 of the nut 21, and which like it has a screw thread 41 onits internal face; the nut 121 is pushed back into the cavity 12, and onit can be seen an outer part 42 and an inner part 43, in thecontinuation along the axis of the machine, and both cylindrical, theouter part 42 being more slender than and separated from the other by acollar 44 acting as a stop face (facing forward) and which touches acorresponding stop collar 45 produced on the stub shaft 113 in thecavity 12 not far from the end face 18. The outer part 42 extendsforward until it projects from the stub shaft j 113, and its end has ascrew thread 46 engaged in the thread 41 of the stop ring 117, and theinner part 43 at its rear end bears a circle of teeth 31 analogous orsimilar to those already described and which mesh with the teeth 30 ofthe locking piece 124.

It can be seen that removing the high-pressure compressor will be farswifter because all that will be required will be for the high-pressureturbine 7 and its shaft 33 to be removed, followed by the locking piece124, gripping it by the flexible tabs 27, in order to be able to unscrewthe nut 121 which will also be extracted from the rear of the machine.The high pressure compressor 5 and its stub shaft 113 may then beremoved by a backward movement, leaving the stop ring 117 in placeagainst the bearing 14. Reassembly will be done by the reverseoperations.

There is no restriction dictating the use of locking parts analogous tothe known part 24: one example of a substitute locking part bears thereference 224 in FIG. 5; it can be distinguished from a the previousones in that the flexible tabs 27 extending axially are replaced by tabs47 in the shape of an arc of a circle and which are consecutive along acircumference. Here again, all that is required is for the free ends ofthese tabs 47 to be pressed in order to cause the bent-over end 26 theybear to leave the groove 28 in the stub shaft 13 or 113. Once again,engagement tongues 29 similar to those of the part 24 and which could,incidentally, have also been added to the part 124, have been depicted.Axially extending bridges 48 connect the tabs 47 to the rest of thelocking piece 224, at the opposite end to the curved-over ends 26.

What is claimed is:
 1. Arrangement for retaining a bearing arrangedaround a stub shaft in which is machined a cavity and which is boundedby an end face comprising a ring forming a stop for the bearing, whichcomprises: a nut for clamping the ring and a locking piece for lockingthe nut, the locking piece being held in the cavity of the stub shaft byremovable means of attachment and connected to the nut by imbricatedteeth arranged in a circle on the nut and on the locking piece, whereinthe ring comprises an interior portion covering the end face of the stubshaft as far as the cavity and equipped with a screw thread for screwingonto a thread of the nut, and wherein the nut is positioned in thecavity and comprises a stop face directed towards the end face andengaged against a stop face standing up from the stub shaft in thecavity.
 2. An arrangement for retaining a bearing according to claim 1,wherein the nut comprises a slender outer part and a thick inner partwhich are separated by a collar constituting the stop face, the outerpart bearing the screw thread and the inner part bearing the circle ofteeth.
 3. An arrangement for retaining a bearing according to one ofclaims 1 or 2, wherein the attachment means comprise flexible tabs withcurved-over ends on the locking piece, said tabs being at the oppositeend to the circle of teeth, and a groove for housing the curved overends being machined in the cavity.
 4. An arrangement for retaining abearing according to claim 3, which comprises tool engagement tonguesarranged on the flexible tabs, in proximity with the curved-over ends.5. An arrangement for retaining a bearing according to claim 3, whereinthe flexible tabs are axial.
 6. An arrangement for retaining a bearingaccording to claim 3, wherein the flexible tabs form an arc and arearranged consecutively on a circle.
 7. An arrangement for retaining abearing according to claim 1, wherein the arrangement is adopted for usein a turbomachine, the stop shaft being secured to a high-pressurecompressor and an end face thereof faces towards a low-pressurecompressor, the bearing supporting the stub shaft by way of a casing.